Ion-channeling study of single-crystal YBa₂Cu₃Oₓ

We have performed Rutherford backscattering spectroscopy and axial ion channeling on superconducting single crystals of YBa₂{Cu}₃Oₓ. Single-crystal platelets with dimensions of more than 2 mm along the a and b axes were prepared by a partial-melt growth technique. Angular profiles of the channeling yield and surface-peak intensities were measured individually for Y, Ba, Cu, and O. A minimum yield of 3.5 for channeling of 1.66-MeV He⁺ ions along the c axis was observed on a crystal with an area of 0.5 mm². Analysis of the results demonstrates that the crystallinity and stoichiometry of the as-grown samples is quite good to within about one nanometer of the surface. The surface-peak intensities indicate surface disorder equivalent to roughly one molecular monolayer. The surface order is quite insensitive to prolonged exposure to room air.